From: Johan Hovold johan@kernel.org
stable inclusion from stable-5.10.80 commit edc546625456da4cc1968086b5a76143fbb0c75d bugzilla: 185821 https://gitee.com/openeuler/kernel/issues/I4L7CG
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=...
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commit 211cde4f5817dc88ef7f8f2fa286e57fbf14c8ee upstream.
Commit 868f3ee6e452 ("serial: 8250: Add 8250 port clock update method") added a hack to support SoCs where the UART reference clock can change behind the back of the driver but failed to add the proper locking.
First, make sure to take a reference to the tty struct to avoid dereferencing a NULL pointer if the clock change races with a hangup.
Second, the termios semaphore must be held during the update to prevent a racing termios change.
Fixes: 868f3ee6e452 ("serial: 8250: Add 8250 port clock update method") Fixes: c8dff3aa8241 ("serial: 8250: Skip uninitialized TTY port baud rate update") Cc: stable@vger.kernel.org # 5.9 Cc: Serge Semin Sergey.Semin@baikalelectronics.ru Tested-by: Serge Semin fancer.lancer@gmail.com Reviewed-by: Serge Semin fancer.lancer@gmail.com Acked-by: Andy Shevchenko andriy.shevchenko@linux.intel.com Signed-off-by: Johan Hovold johan@kernel.org Link: https://lore.kernel.org/r/20211015111422.1027-2-johan@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Chen Jun chenjun102@huawei.com Reviewed-by: Weilong Chen chenweilong@huawei.com Acked-by: Weilong Chen chenweilong@huawei.com
Signed-off-by: Chen Jun chenjun102@huawei.com Signed-off-by: Zheng Zengkai zhengzengkai@huawei.com --- drivers/tty/serial/8250/8250_port.c | 21 +++++++++++++++++---- 1 file changed, 17 insertions(+), 4 deletions(-)
diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c index 5d40f1010fbf..110a19c5138e 100644 --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -2675,21 +2675,32 @@ static unsigned int serial8250_get_baud_rate(struct uart_port *port, void serial8250_update_uartclk(struct uart_port *port, unsigned int uartclk) { struct uart_8250_port *up = up_to_u8250p(port); + struct tty_port *tport = &port->state->port; unsigned int baud, quot, frac = 0; struct ktermios *termios; + struct tty_struct *tty; unsigned long flags;
- mutex_lock(&port->state->port.mutex); + tty = tty_port_tty_get(tport); + if (!tty) { + mutex_lock(&tport->mutex); + port->uartclk = uartclk; + mutex_unlock(&tport->mutex); + return; + } + + down_write(&tty->termios_rwsem); + mutex_lock(&tport->mutex);
if (port->uartclk == uartclk) goto out_lock;
port->uartclk = uartclk;
- if (!tty_port_initialized(&port->state->port)) + if (!tty_port_initialized(tport)) goto out_lock;
- termios = &port->state->port.tty->termios; + termios = &tty->termios;
baud = serial8250_get_baud_rate(port, termios, NULL); quot = serial8250_get_divisor(port, baud, &frac); @@ -2706,7 +2717,9 @@ void serial8250_update_uartclk(struct uart_port *port, unsigned int uartclk) serial8250_rpm_put(up);
out_lock: - mutex_unlock(&port->state->port.mutex); + mutex_unlock(&tport->mutex); + up_write(&tty->termios_rwsem); + tty_kref_put(tty); } EXPORT_SYMBOL_GPL(serial8250_update_uartclk);